People with post-traumatic stress disorder (PTSD) process sad, non-traumatic memories differently to traumatic memories, new research suggests.
People with PTSD experience intrusive, recurrent flashbacks of traumatic events that are often accompanied by high levels of anxiety and emotional distress.
When people with PTSD experience a flashback, they feel as though they're experiencing the traumatic event again in the present moment, rather than thinking back on it like a typical memory. Now, scientists think they may know why.
A new study in patients with PTSD, published Thursday (Nov. 30) in the journal Nature Neuroscience, revealed that sad, non-traumatic memories are processed in a part of the brain called the hippocampus, while the traumatic memories associated with PTSD activate a region above it known as the posterior cingulate cortex (PCC). Although both brain regions are involved in memory and emotional processing, the PCC is more focused on internally directed thought, such as daydreaming or being aware of one's thoughts and feelings.
By comparison, the hippocampus is responsible for organizing and contextualizing memories.
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In the study, the authors wanted to explore what happens in the brain when people with PTSD recall memories. They recruited 28 people with PTSD who recounted three types of memory to a clinician: calm memories, such as walking in a forest; non-traumatic, sad memories, such as the loss of a loved one; and traumatic memories, such as being in a car accident.
Each of these memories was then converted into a script that was read out to patients in two-minute clips while their brains were scanned using a magnetic resonance imaging (MRI) machine. The scans focused on the hippocampus, which helps store long-term memories of events and is also involved in retrieving those memories.
"This brain region is critical for memory, if you have damage in the hippocampus you cannot form new memories," co-senior study author Daniela Schiller, a professor of neuroscience at the Icahn School of Medicine at Mount Sinai, New York, told Live Science.
Patients who had sad, non-traumatic memories that were about the same topic had similar levels of activation in the hippocampus to each other. "What it tells us is that the hippocampus cares or is involved because it is sensitive to these degrees of similarity," Schiller said.
However, the same wasn't the case for traumatic memories, which instead activated the PCC. The more severe a patient's PTSD symptoms were, the greater the PCC activity was.
Using a machine learning algorithm, the researchers determined whether a pattern of brain activation corresponded to a sad or a traumatic memory — meaning they could predict what type of memory a patient was experiencing based on activity in their brain.
More research is needed in larger groups of people, the authors wrote in the paper. However, they hope that the findings could lead to the development of new therapies that tweak brain function to turn these traumatic memories into ones that more closely resemble non-traumatic memories.
"If we find that sad memories are in the hippocampus and these are memories that are not disruptive to you, treatment could aim to make these traumatic memories more like regular memories," Schiller said.
"If treatment works, maybe we will see that they engage the hippocampus when they become more benign," she said.
However, these are currently still aspirations, so it may be a while before any such treatment is available.
This article is for informational purposes only and is not meant to offer medical advice.
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